this question gets a greater scope if related not only to a flash plugin inside Firefox, but to the larger issue of avoiding high use of resources (GPU) through use of external players to play embedded flash in general. see this answer and comments (askubuntu.com/a/169298/47206)
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cipricusJul 28 '12 at 21:55

3 Answers
3

VLC can play any Flash video for which you have the .flv file. It can also record anything it is playing.

However, you can't always just point it at a webpage and play Flash videos on that page and it can't 'play' .swf files (because they aren't videos). You need to somehow download the .flv file. There are tools that work for some sites such as cclive, get_iplayer and youtube-dl that download the .flv files.

Not all sites are supported by such tools but there is a work around that allows you to download the video file so that you can watch it without using Flash for the actual watching although you do need the Flash plugin installed to do this. This workaround uses Chromium but a similar method works with Firefox+Firebug.

In Chromium, press Ctrl+Shift+J to open the developer console and click on the 'Network' tab.

Then, navigate to the page with the video on and start to play it. You can then look for the item in the list with a type starting with 'video/' and click on it.

This will give you a URL which you can copy and download using wget or a download manager.

Once you have copied the url, you can close the page which will stop Flash from running.

This works for any non-live Flash video as long as additional digital restrictions management methods (like RTMP used on BBC iPlayer) are not used.

Live Flash streams such as Ustream are, as far as I know, not possible to play with VLC. However, some sites may give you a proper streaming URL like an mms or rtsp link which VLC can play.

Get FlashVideoReplacer. The extension automatically replaces embedded flash videos with the original mp4 or flv videos, allowing to watch flash streaming content with a less CPU intensive plugin or standalone external player.

Keep in mind that although VLC is an excellent player, the plugin isn't. FVR won't work well with VLC plugin. The recommended plugin is gecko-mediaplayer. For documentation, supported sites and tweaks see the extension web site

As stated in another answer, VLC will play the URL stream behind an embedded video.

I prefer the solutions that involve the use of Firefox addons that normally direct an URL to a download manager or to another browser but that can be set to select VLC instead. When there is a link that can be clicked and that goes directly to the video stream, like in Youtube, I prefer something like the Openwith addon (see below). But sometimes there is no such link.

(The selected answer there is by no means the best. The most voted one, which is similar to the one under here already mentioned, is good because it involves using just the Chrome browser. But it does not work with all streams, and neither does the Firebug addon for Firefox, as far as I can tell.)

Maybe the more convenient solution is using VLC along the Firefox FlashGot addon

add VLC to Flashgot list: FlashGot options, General tab, Add, give a name 'VLC' , - then go to the VLC executable and select it.

FlashGot options, FlashGot tab, choose VLC

playing the video in Firefox, a Flashgot button should appear (add that to the toolbar or the status bar). Right-click the button, Available formats, and left-click the video. VLC should start playing the video stream.

VLC + the Video DownloadHelper

the addon for Firefox - that I mentioned in my answer there, just install the addon, play the stream, the DownloadHelper button should start rolling, click the drop-down menu, then put the mouse over the title of the video, and then choose 'Copy URL'. (The download option is there of course, but that's another issue.)

Open VLC, Ctrl-N and then paste and open the URL.

Some troubleshooting:

Testing such links with VLC I notice that in some cases the player cannot play them or even crashes. But this can be fixed as follows:

The last part of such URLs is sometimes like /video.flv?start=0. Changing that to /video.flv? might make it work. (But in many cases the stream is played very well without this change. Also, in many cases the link may look completely different anyway.)

To start youtube videos (and alike: dailymotion, etc) in external players I think that the best solution is to use the Firefox Openwith addon and just add vlc instead of/beside browsers.
And it works perfectly